Injection devices include a nozzle removably connected to the tip of a heating cylinder. In an injection molding process, the nozzle is brought into contact with a molding die and a molten material is injected from the injection device into a cavity of the molding die. The nozzle has design factors, such as an outside diameter, length, and material, which are to be changed depending on the type of the molding die with which the nozzle is used in combination. To meet with this requirement, many different types of nozzle are prepared in advance and one nozzle selected from among the prepared nozzles is threadedly attached to the tip of the heating cylinder.
According to a prior improvement shown in Japanese Patent Publication (JP-B) No. 05-29535, a nozzle adaptor is used, which enables use of several different nozzles in combination with a single heating cylinder.
FIG. 7 hereof shows a general configuration of a heating cylinder head disclosed in JP 05-29535 B. The disclosed heating cylinder head includes a nozzle 101 and a nozzle adaptor 102 that are threadedly connected together. The nozzle adaptor 102 has a pair of diametrically opposite pin holes 103, 103 formed on a front surface thereof. A separately provided handle member 104 includes a central tubular hub 105 having a pair of diametrically opposite pins 106, 106 projecting from one end face of the tubular hub 105 for fitting engagement with the pin holes 103, 103, respectively, and a pair of arms 107 extending radially outwardly from the tubular hub 105 in diametrically opposite directions.
With the pins 106, 106 of the handle member 104 being fitted in the pin holes 103, 103 of the nozzle adaptor 102, the handle member 104 is rotated in a screw tightening direction so that the nozzle adaptor 102 can be screwed onto the tip of a heating cylinder 108. The handle member 104 is a large-sized special jig and, hence, is not easy to store. The nozzle 101 threadedly fastened to the nozzle adaptor 102 can be replaced with another nozzle when necessary. However, JP 05-29535 B has no disclosure or teaching about how and where attachment and detachment of the nozzle 101 relative to the nozzle adaptor 102 is performed. It may be considered that such attachment/detachment of the nozzle 101 relative to the nozzle adaptor 102 is achieved at an assembly site which is provided separately from a molding site and which is furnished with various tools and jigs.
To deal with an increasing demand for a little production of many kinds of molded articles, it is desirable that both attachment/detachment of the nozzle adaptor 102 relative to the tip of the heating cylinder 108 and replacement of the existing nozzle 101 with a different nozzle can be achieved at a molding site without reliance on the use of a large-sized jig.
It may be considered that a nozzle is configured to have a wrench engagement part on its outer peripheral surface so as to facilitate attachment/detachment relative to the nozzle adaptor. However, the wrench engagement part makes it difficult to arrange a heater in such a manner as to surround uniformly over the entire area of the outer peripheral surface of the nozzle. Due to a local low temperature area created by the presence of the wrench engagement part, an appropriate control of the nozzle temperature cannot be achieved.
It is accordingly an object of the present invention to provide an injection device having a two-piece nozzle composed of a nozzle adaptor and a nozzle body which can be assembled and disassembled at a molding site without using a large-sized jig.
Another object of the present invention is to provide a jig for use in assembling and disassembling the two-piece nozzle.
A further object of the present invention is to provide a method of assembling the two-piece nozzle, which is particularly suitable for a little production of many kinds of molded articles.